Gas-filled discharge tube system



GAS FILLED DISCHARGE TUBE SYSTEM Filed April 9, 1955 7.5 7;. Grid bias76 0 U. Grililzias g 40 c 77 S E 1 0Zts an External Electrode INVENTORJPRazicgiLlffi E BY J? LiE' wards ATTORNEY Patented May 5, 1936 UNITEDSTATES GAS-FILLED DISCHARGE TUBE SYSTEM John P. Radcliff, Bloomfield,and Paul Grifiith Edwards, Verona, N. J., assignors to AmericanTelephone and Telegraph Company, a corporation of New York ApplicationApril 9, 1935, Serial No. 15,481

4 Claims.

This invention relates to thermionic tubes of the type containing gasand depending upon the ionization of the molecules of the gas foroperation, and more particularly relates to a method 5 of and means forcontrolling the operation or breakdown voltage of tubes of this type.

At present thermionic or gas-filled discharge tubes consist essentiallyof an envelopecontaining a cathode and an anode, and in many instances agrid which is used to control the passage of current from the cathode tothe anode. These elements are immersed in a gas which will vary innature and pressure depending upon the duty for which the tube isdesigned. One of the primary objects of this invention consists inproviding a method of controlling the breakdown or operating voltage oftubes of this type which is electrostatic in nature. The electrostaticmethod of this invention for controlling the operation or breakdownvoltage of ionic tubes, so that the tube may be started in operation,'may be employed either for primary or secondary control, that is tosay, the electrostatic control may be employed as the main source ofcontrol of the tube or as a means for modifying the action of the tubewhen the said tube is to be controlled by some other means, such as bythe voltage applied to the grid. Other objects and features of theinvention will appear more fully from the detailed description thereofhereinafter given.

The invention may be more fully understood. from the followingdescription together with the accompanying drawing, in the Figures 1, 2,3, 4 and 5 of which the invention is illustrated.

Fig. 1 is a diagrammatic showing of a gasfilled discharge tube embodyingcertain of the arrangements of the invention. Figs. 2 and 3 are planviews of Fig. 1 together with certain circuit arrangements of theinvention. Fig. 4 is a plan view of a tube which shows a modification ofthe invention. In Fig. 5 are shown graphically certain features ofoperation of the invention. Similar reference characters have been usedto denote like parts in all of the figures.

In Fig. 1 is shown a gas-filled discharge tube having a glass envelopeI. Within the tube and mounted on a stem are shown a cathode 3, a grid 4and an anode 5. The cathode is of the solid heated thermionic emittingtype. In Fig. 2 the 50 battery 1 serves as the source for heating thecathode. The grid 4 may be cylindrical and have a small opening thereinand will surround the cathode. The bias on the grid may be varied by theadjustable resistance 8 and battery I. Between the cathode 3 and theanode 5 is provided a source of potential, such as the battery 9. Thevoltage of battery 9 should be below the normal breakdown voltage of thetube but above the voltage needed to sustain a discharge in the tubeafter it has broken down, or started to discharge. In accordance withthe arrangements of this invention, the tube is provided with anexternal electrode 2. This may be affixed to the outside of the glassenvelope, if desired, and may be in various forms. A desirable form isto make it of a metal band, for example of brass, surrounding the tube.However, other forms and materials may be usedfor the externalelectrode. In accordance with the arrangements of this invention thebreakdown voltage of the tube may be varied by applying diiferentcharges of potential to the external electrode. Thus the externalelectrode, when a charge is applied thereto, may be used either forexercising primary or secondary control over the operation of the tubeand accordingly may be used to start'a continuous discharge in an inerttube.

In Fig. 2 is shown a circuit arrangement whereby the external electrodemay be used for starting a continuous discharge in the tube. Asheretofore pointed out the battery 8- interconnecting the anode 5 andcathode 3 will be of a potential above the voltage needed to sustain thetube in operation but below the voltage'needed to cause the tube tobreak down. The external electrode 6 will be connected to a switchingdevice 1 When the switch 1' is operated a charge will suddenly beapplied from the device 8' capable of supplying the desired voltage tothe external electrode 2 and will result in causing the tube to breakdown and discharge. The charge on the external electrode 2 may beremoved by operating the key to the grounded contact shown. In otherwords a gas-filled tube of the type having a solid heated thermionicemitting cathode may in accordance with the arrangements of thisinvention be started in operation by the establishment of anelectrostatic field in the vicinity thereof. A load l5 in thecathode-anode circuit is shown. The tube arrangements may of course beused for many things, suchfor example as a relay device.

In Fig. 5 the effect of the establishment of an electrostatic field onthe operating or firing voltage is illustrated graphically. The curvesl6 and F I! show the relationship in certain type of tube utilizedbetween the firing or breakdown voltage and the voltage applied to theexternal electrode. Curve I 6 shows the relationship when the bias onthe grid is 1.5 volts, while the relationship without any bias on thegrid is shown by curve I 1. For example, from curve I 6 it will be seenthat with a grid bias voltage of 1.5 volts the anode voltage necessaryto permit firing was reduced from a normal of 84 volts with no charge onthe external electrode, to 65 volts with a charging potential of 112.5volts on the external electrode.

In Fig. 3 is shown a view of the same tube as shown in Figs. 1 and 2with circuit arrangements whereby the tube could be caused to start acontinuous discharge by other means than the switch 1 shown in Fig. 2.In Fig. 3 the external electrode 2 is connected by conductor 6 to thefixed plate ll of a condenser I0. The other plate I 2 of condenser I isconnected to the variable source of potential'8 and may be bent orwarped in the manner of a diaphragm by means of the magnet l3 in acontrol circuit M. An impulse sent over circuit M will, accordingly,change the relationship between the plates of condenser l0 and suddenlyvary or apply a charge-to the external electrode 2. This will serve tostart the tube in operation with a continuous discharge.

In Figs. 1, 2 and 3 tubes having three internal electrodes have beenillustrated. However the arrangements of the invention are applicable toother types of tubes having solid heated thermionic emitting cathodes.For example, the grid electrode might be omitted as shown in Fig. 4. Theheated cathode in this arrangement is shown as 3 and the anode as Inthis arrangement the anode may be in plate form if desired. The onlydifierence in this tube would be the lack of any grid or biasing effect.Furthermore, tubes having cathodes with an auxiliary heater device mightequally well be utilized in the arrangements of the invention.

While the invention has been disclosed as embodied in certain specificarrangements which are deemed desirable it is understood that it iscapable of embodiment in many and other widely varied forms withoutdeparting from thespirit of the invention as defined by the appendedclaims.

What is claimed is:

l. A gas-filled discharge tube including cathode and anode electrodeswithin an envelope containing gas at low pressure, said cathode being ofthe solid heated thermionic emitting type, a circuit including a directcurrent source interconnecting said electrodes, the voltage of saidsource being below the breakdown voltage of said tube but above thevoltage needed to sustain a discharge therein after breakdown, a thirdelectrode external to said envelope, and means for causing a differenceof potential to exist between said external electrode and one of saidother electrodes whereby a continuous discharge may be started in saidtube.

2. A gas-filled discharge tube including cathode and anode electrodeswithin an envelope containing gas at low pressure, said cathode being ofthe solid heated thermionic emitting type, a

ci rcuit including a direct current source interode, anode and gridelectrodes within an envelope containing gas at low pressure, saidcathode being of the solid heated thermionic emitting type, a circuitincluding a direct current source inter connecting said cathode andanode electrodes, the

voltage of said source being below the breakdown voltage of said tubebut above the voltage needed to sustain a discharge therein afterbreakdown, adjustable means for applying biasing potentials to said gridelectrode, a fourth electrode external to said envelope, and adjustablemeans for suddenly applying a. desired voltage to said fourth electrodeto cause a continuous discharge to start in said tube.

4. A gas-filled discharge tube including cathode and anode electrodeswithin an envelope containing gas at low pressure, said cathode being ofthe solid heated thermionic emitting type, a circuit including a directcurrent source interconnecting said electrodes, the voltage of saidsource being below the breakdown voltage of said tube but above thevoltage needed to sustain a discharge therein after breakdown, a thirdelectrode external to said envelope, a condenser having a fixed plateand a movable plate, means for connecting said fixed plate to said thirdelectrode, variable means for causing a difference of potential to existbetween the plates of said condenser, and means for suddenly moving themovable plate of said condenser to vary the charge on said thirdelectrode whereby a continuous dis- 5 charge may be started in saidtube.

JOHN P. RADCLIFF. PAUL GRIFFITH EDWARDS.

